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SubjectRe: Incorrect UDMA timing on VIA vt82c596b
On Tue, Oct 10, 2000 at 01:10:06AM -0700, Andre Hedrick wrote:

> These are two different issues.
> One is host side detection and the other is drive side
> detection/acknowledgement.
>
> ide0=ata66 overrides the host-rules
>
> ivb-byte93 overrides the mixed drive side rules.
>
> The only think that is safe to do is allow users to randomly fake the
> driver over the 80c ribbon issue, but if te drive fails to sense the
> capacitance it must reject the attempt because of the iCRC and normal high
> penality of resets/downgrades t oa stable signal clock.

Yes, but there is often the scenario where you have an UDMA66 capable
drive and a say ZIP drive which makes the 80c cable undetectable by the
drive. In that case a command line option would help, so that the kernel
doesn't have to be recompiled for that.

I think it'd be good to think of 'ide0=ata66' as an option that disables
all the 80-wire checks and consider that option dangerous, but still
very useful.

If you could get the byte93 stuff correct, I'd agree with you that the
'ide0=ata66' should not mess with it, but it's impossible to get it
correct due to devices like IOMEGA ZIP.

> Have you read the Quantum ammendments to the signal level thresholds?

Well, yes.

> The crosstalk can cause mis-clocks and data-corruption. I will bet you
> that these were systems that if you pull that drive out and put it into a
> standard system it will fail. Those are special case where an OEM has a
> drive maker adjust the skew tables to allow dirty tricks.

I'll have to try that.

--
Vojtech Pavlik
SuSE Labs
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